Researchers have successfully created an all-polymer solar cell, …

Share this story

Polymer-based solar cells have received a fair bit of attention in the research community, some of which has been covered here at Nobel Intent. Much of the attraction is in being able to move away from the expensive raw materials used in inorganic solar cells and the costly manufacturing that accompanies them. Researchers have recently demonstrated an all-organic solar cell with a high efficiency, one that can provide both thin and flexible solar cells and routes to cheap manufacturing.

Much of the coverage of solar cells is focused on the material doing the dirty work of converting energy from incoming photons into usable electrons, which is a main factor behind the efficiency and properties of the cell. But an anode and cathode are also needed to create a complete, functioning photovoltaic cell, and this is where the research focused. The anode needs to be transparent across the full spectrum of visible light while being highly conductive. This has historically meant indium tin oxide (ITO), even in "organic" solar cells. Although effective, ITO is brittle and uses expensive indium, making it a target for a replacement material.

Electrically conductive polymers have been continually improving over the years, and have finally reached a place where they have acceptable conductivity to be up to the task of acting as the anode of a photovoltaic device. Researchers used the polymer PEDOT:PSS as an anode, fabricating a complete photovoltaic device using a relatively simple spin-coating process to create the various functional layers; the cathode was made through an evaporation of aluminum and calcium.

The device showed performance drops of less than 0.5 percent compared to the same device fabricated with an ITO anode, marking what is believed to be the highest efficiency in a polymer anode solar cell. The use of a polymer substrate rather than glass was also investigated, with performance drops of roughly 0.1 percent reported when compared to the ITO cell.

Even more important is the mechanical stability of an all-polymer device. After only 75 bending cycles, an ITO anode cracks enough that the device no longer functions. The all-polymer cells went through 300 bending cycles with no decrease in performance, making these the most robust solar cells around.

Although the absolute performance of an all-polymer solar cell (about 2.8 percent efficiency) pales in comparison to the state-of-the-art silicon cells (which can top 15 percent efficiency), this is still a noteworthy accomplishment for cheap, clean energy generation. An all-polymer cell has the potential to be fabricated using techniques like roll-to-roll processing (think newspaper printing press), which would provide supremely cheap organic electronic devices. The combination of price/watt efficiency and the ability to take the punishment of applications outside of a dedicated solar array promises that polymer solar cells are likely to play an important roll indeed.